1. Field of the Invention
The present invention relates to a recording medium used in an information processing apparatus applying the STM technique.
2. Related Background Art
In recent years, a scanning tunneling microscope (STM) that allows the observer to directly observe the electron structure of the surface atom of a conductor was developed (G. Binnig et al., Phys. Rev. Let., 49, 57 (1983)) to enable measurement of a real space image with a high resolution regardless of whether the sample is monocrystalline or amorphous.
This STM exploits the fact that, if a voltage is applied across a metal tip and a conductive material, and the distance between the two is decreased to about 1 nm, a tunneling current flows between them.
This current is very sensitive to changes in distance between the tip and the conductive material, and it changes exponentially. By scanning the tip to keep the tunneling current constant, a surface structure in real space can be observed at a resolution in the atomic order.
The above-mentioned apparatus or means detects a weak current,. so that the surface structure can be advantageously observed with a small power without damaging the medium.
Since the above apparatus can operate in the atmosphere, observation evaluation using the STM technique is widely performed for biological samples, organic molecules, and the like in the atomic or molecular order. Recently, also in the field of industries, given the fact that the STM has spatial resolution in the atomic or molecular size, its application to a recording/reproducing apparatus and its practical use are prevalent (Japanese Laid-Open Patent Application Nos. 63-161552 and 63-161553).
In information processing by this apparatus, information is recorded on the surface of a sample medium by any electrical method while sweeping the tip parallel to the sample surface, and the recorded information is reproduced by measuring a physical phenomenon (e.g., a tunneling current) caused upon approach of the tip to the sample.
In this case, to smoothly record/reproduce information, information must be recorded on the sample with certain regularity. For this purpose, e.g., tracking information (e.g., microstructures) is required on the sample.
However, the recording surface of the sample medium usable for recording/reproducing information in the atomic or molecular size must be flat at the atomic or molecular level. The tracking information must be formed with an atomic- or molecular-level precision without degrading the surface flatness.
As a method capable of tracking at the atomic or molecular level, a method of recording/reproducing information along the regular orientation direction of crystal lattices of a sample medium is proposed (Japanese Laid-Open Patent Application No. 4-241240).
In this method, however, each atom in the crystal face must be recognized, which requires a high detection precision. As a result, the scanning speed decreases. Further, this method cannot be used for a sample medium not having any regular crystal lattice.